Device to prevent accidental ignition of electro-explosives from electrostatic discharge

ABSTRACT

Conductive structure connected to a electroexplosive device casing and extending into close proximity to igniter electrical lead wires at a place where discharge of stray electrostatic charges across a spark gap from one or both of said lead wires to the conductive means will not cause ignition of the electroexplosive devices.

Unite- Staes FROM ELECTROSTATIC DISGE Inventor: John T. Petrick,Fredericksburg,

The United States of America as represented by the Secretary of theNavy, Washington, DC.

Filed: Mar 30, 1972 Appl. No.: 239,527

Assignee:

References Cited UNITED STATES PATENTS 8/1961 Franklin 102/28 @gggtf 19[11] 3,78,762

Petrick Feb. 5, 1974 [5 DEVICE TO PREVENT ACCIDENTAL 3,264,989 8/1966Rucker 102/28 IGNH'ION 0F ELECTRO EXPLOSIVES 3,333,538 8/1967 Schnettler102/28 FOREIGN PATENTS OR APPLICATIONS 538,331 3/1957 Canada ..102 28768,486 2/1957 Great Britain ..102/28 Primary ExaminerVerlin R.Pendegrass 57 ABSTRACT Conductive structure connected to aelectroexplosive 2 Claims, 9 Drawing Figures PAIENIEDFEB 5W4 3;?89J'62SHEET 2 UP 2 FIG. 7 F/G. 6

T0 PULSE FIRING GENERATOR 40 TO EED LEADS\ FIG. .9

DEVICE TO PREVENT ACCIDENTAL IGNITION OF ELECTRO-EXPLOSIVES FROMELECTROSTATIC DISCHARGE BACKGROUND OF THE INVENTION A. Field of theinvention The present invention relates generally to electroexplosivedevices and more particularly to means to prevent electrostaticallycaused discharges from accidentally igniting electroexplosive devices.

B. Description of the prior art.

Previous methods for eliminating the electrostatic hazards toelectroexplosive devices have generally been aimed at producing lesssensitive devices. There are, however, many weapons in use today whichnecessitate the use of more sensitive electroexplosive devices. Thus,handling of these weapons and especially the handling of the sensitiveelectroexplosive devices is a hazardous operation.

The concept of discharging electrostatic charges by a spark gap from anelectrical lead to the electroexplosive device casing is well known, butthe structures heretofore used to accomplish this result are, for themost part, too complex, and cannot be added to existing electroexplosivedevices without extensive modifications to the electroexplosive devices.

SUMMARY OF THE INVENTION The invention provides a simple and versatilemeans to prevent electrostatic charges from accidentally ignitingelectroexplosive devices.

OBJECTS OF THE INVENTION An object of the present invention is to rendersensitive electroexplosive devices safe from inadvertant ignition due tostatic electricity without drastically changing the electroexplosivedevice design.

Another object is to provide means for making sensitive electroexplosivedevices safe which is easily adaptable to existing electroexplosivedevices.Other objects, advantages, and novel features of the presentinvention will become apparent from the following detailed descriptionof the invention when considered in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top view of anelectroexplosive device utilizing a first embodiment of the presentinvention;

FIG. 2 is a front view of FIG. 1;

FIG. 3 shows the foil tab of the first embodiment before it is employedon an electroexplosive device;

FIG. 4 is a side view of FIG. 3;

FIG. 5 is a top view of a second embodiment of the present invention;

FIG. 6 is a front view of FIG. 5;

FIG. 7 is a front view of a third embodiment of the present invention;

FIG. 8 is a side view of FIG. 7; and

FIG. 9 is a cross-sectional view of a fourth embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIGS. 1 and 2 show anelectroexplosive device having a casing 18 which contains an explosivemixture in the lower part thereof. Lead wires 11 and 12 leading throughan insulating Plug 17 into the explosive mixture are are connectedthereat by a bridge-wire l9. Foil tab 13 has a conductive foil withconductive adhesive 14 on one side thereof as shown in FIG. 4. The foiltab 14 is originally flat as seen in FIG. 3. When applied toelectroexplosive device 10, the adhesive is stuck to plug member 17 andis folded down at 13 to touch casing 18, as best illustrated in FIG. 2.Static charges are thereby conducted from the foil tab 13 to the casing18 or vice versa. Lead wires 11 and 12 have bare spots, not shown, wherethe insulation has been removed at spark gaps 15 and 16 adjacent thepointed portions of foil 13.

The metallic foil typedevice provides electrostatic discharge protectionby allowing an electrostatic discharge, characterized by a high voltagetransient accompanied by a spark, to pass from one lead wire to theother by means of a spark occurring at the gaps 15 and 16 as shown inFIG. 1. Also, protection for an electroexplosive device having anelectrostatic discharge passing through both wire leads 11 and 12 isgiven by sparks occurring at the same gaps, l5 and 16 in FIG. 1, whichshort circuits the electrostatic discharge to the electroexplosivedevice casing 18. Since at notime does the discharge pass through theelectroexplosive device bridge-wire 19 or explosive mixture, there is.little chance for the electroexplosive device to initiate.

The embodiment of FIGS. 5 and 6 shows an electroexplosive device 20which has a casing 28 with an explosive mixture in the bottom portionthereof. Leads 21 and 22 extend through insulating plug 27 and connectwith bridgewire 29 which is incontact with the explosive mixture.Threaded needle points 23 and 24 are threaded into the insulating plug27 preferably through casing 28. Needle points 23 and 24 areelectrically grounded to casing 28 in any suitable fashion such as merecontact. Lead wires 21 and 22 have the insulation removed at the pointnearest needle points 23 and 24, that is at spark gaps 25 and 26.

The needle point type device provides electrostatic discharge protectionby allowing an electrostatic discharge to pass from one lead to anotherby means of sparks occurring in the spark gaps 25 and 26 as seen in FIG.5. This device also protects an electroexplosive device having anelectrostatic discharge passing through both wire leads 21 and 22 bysparks occurring at gaps 25 and 26 which short circuit the electrostaticdischarge to the casing 28. Therefore, no discharge passes through thebridge-wire 19 or the explosive mixture so the electroexplosive devicecannot be accidentally fired by static electricity.

FIGS. 7 and 8 show another embodiment of the present invention whereinan extension 32 at one end of electroexplosive device casing 31 is anintegral part of the casing. Once an insulating plug with lead wiresextending therethrough is placed-in the top of electroexplosive device30, as in the previously discussed embodiments, tab extension 32 isfolded over so that pointed portions 33 and 34 are near the lead wiresto form a spark gaps therebetween. The lead wires, not shown, as in theother embodiments, have insulation removed near pointed portions 33 and34 of extension 32 at the spark gaps, not shown. The function of thisembodiment is the same as in the previous embodiments discussed above.

FIG. 9 is a remote protective device embodying the present inventiveconcept. Lead wires 41 and 42 pass through insulating block 57 andextend to the electroexplosive device lead wires. Wire 43 is connectedto needle point 44 and to the electroexplosive device metal casingground. The remote protective device 40 of FIG. 9 may be placed at anyreasonable distance from the electroexplosive device associatedtherewith. Metal discharge needle 45 is pointed at both ends and isfixed by any suitable means, such as a set screw, so as to form sparkgaps 46 and 47 when lead wires 41 and 42 are inserted in the insulatingblock with the insulation removed at the point adjacent the needlepoint. Partially threaded upper discharge needle 44 is adjacent leadwire 41 and forms a spark gap 48 between the point of needle 44 and theclosest portion of lead wire 41 where the insulation has been removed,though the missing insulation is not illustrated in the drawing.

Obviously many modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstood that, within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. In an electroexplosive device having a casing and a pair of leadwires connected by a bridge wire in a body of explosive material, thesafety improvement comprising:

an exteriorly disposed electrically conductive foil member connected tosaid casing by an electrically conductive adhesive and having pointedportions thereof adjacent said lead wires to form spark gaps betweensaid lead wires and said foil member, wherein said spark gaps areinsulated from said explosive material.

2. The device of claim 1 wherein said spark gaps are insulated by aninsulating member received in said casing.

1. In an electroexplosive device having a casing and a pair of leadwires connected by a bridge wire in a body of explosive material, thesafety improvement comprising: an exteriorly disposed electricallyconductive foil member connected to said casing by an electricallyconductive adhesive and having pointed portions thereof adjacent saidlead wires to form spark gaps between said lead wires and said foilmember, wherein said spark gaps are insulated from said explosivematerial.
 2. The device of claim 1 wherein said spark gaps are insulatedby an insulating member received in said casing.